In the scope of practical application of the this invention, the following patents are known: U.S. Pat. Nos. 7,259,341, 7,388,484, 7,292,145, 7,170,403 y 4,599,498, related to security systems and detection of intrusion in split case devices. In this sense, the financial entities impose security requirements which the devices related to financial transactions such as PIN pads, payments terminals, etc., must fulfill, since this kind of devices are normally used in insecure environment.
Some security mechanisms that detect the opening of a split case device include a switch arrangement that operates in combination with a circuit board held by both split cases of the device. The mechanical force applied by the superior and inferior split case when they are closed maintains a conductive surface of the switch actuator pressed against adjacent conductive traces on the circuit board creating electrical contact between them. The conductive traces are normally connected to tamper detection electronics. When the split case is opened, the switch activator is released interrupting the electrical contact between the conductive traces of the circuit board which detected by an electronic circuit that triggers a terminal intrusion (tamper) response mechanism.
This tamper switch arrangement design does not protect against all attacks, such as those which include sliding a conductive member under the switch actuator with the purpose of maintaining the conducting state between the pads on the circuit board even when the switch actuator is not pressed against the circuit board and the split case is opened. As can be seen in FIG. 1, which is attached to this application, in order to detect these attacks, guard conductors 1 are used arranged around the adjacent conductors on the circuit board.
Even though the protection conductors contribute to the protection from attack described above, the result is not entirely satisfactory as it does not protect against attacks consisting in infusion or injection of conductive ink over the adjacent conductive traces on the circuit board maintaining the electrical connection between them even when the actuator of the intrusion detection switch is not pressed over the circuit board.
Some tamper switch implementations, as shown in FIG. 1, include a segment which seals the space between the actuator and the component in whose interior moves the actuator in order to avoid the infusion of conductive ink through this space over the adjacent electrical conductive traces. This measure is not entirely satisfactory since the segment or the cup could be perforated and therefore allowing an injection of conductive ink over the conductive traces. Normally, these attacks consist in drilling a hole through the casing and the switch to inject through it electrically conductive material 103 under the switch actuator over the adjacent contact pads 102 of the circuit board in order to maintain the electrical contact between them even when the switch actuator is released.
Other tamper switch arrangements, as for example in the solution provided in the U.S. Pat. No. 7,259,341, include an actuator with an open cylindrical portion in which is inserted an aligning pin of the back casing. In these cases it could be possible to access the contacts on the circuit board bellow the actuator by drilling through the casing, its aligning pin and the actuator and to inject a conductive material over the contacts on the circuit board, thereby defeating the tamper detection mechanism.
In other cases it is possible to exercise a compressing external force on a portion of the case on top of the switch to maintain the switch pressed, cut the casing around said portion and open the casing while the switch is maintained pressed.
In general, the current art tamper switch arrangements use two adjacent contacts on a circuit board, which participate in a tamper detection mechanism together with a two state switch. Since any attack that achieves to short-circuit the said adjacent contacts defeats the tamper detection mechanism, until now all efforts have been focused on protecting said adjacent contacts by additional electrical and mechanical measures, making the tamper detection switch arrangements complex, yet not sufficiently effective.